ME/MECA 238A 1

ME/MECA 238A - Mechanical/Mechatronic

Design Project ICourse notes prepared by G.A. Kallio, based on

The Mechanical Design Process, by D.G. Ullman

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Project Planning (Ch. 5)

• Step 1: Identify the tasks– Use WBS (work breakdown structure) or

flowchart network– Be as specific and detailed as possible– Include course-related presentations & reports

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Project Planning, cont.

• Step 2: State objective of each task– What will be the result (deliverable) of each

task?– May be information, a completed drawing,

calculation results, test data, a report, a generated concept, manufactured component, etc.

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Project Planning, cont.

• Step 3: Estimate the personnel, time, and other resources needed to meet objectives– Specify who– Specify work rate (e.g., hours/week)– Specify period of time– Specify total time for each task

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Project Planning, cont.

• Step 4: Develop a sequence for the tasks– Identify precessors and successors for each task– Sequential (series) vs. parallel tasks– Coupled vs. uncoupled parallel tasks– Design structure matrix (DSM)– Identify critical path(s)

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Project Planning, cont.

• Step 5: Estimate the product development costs– Design costs de-emphasized– Material costs are real– Manufacturing costs may be real– Testing costs de-emphasized

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ISO-9000

• International Standards Organization’s quality management system

• Standardized documentation of the product development process

• ISO-9000 certification – similar to University accreditation – indicates to the world that product quality is managed, controlled, and assured by the ISO

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Concept Generation (Ch. 7)

• A concept is an idea or “structure” that is sufficiently developed to – evaluate the physical principles that govern its

behavior – evaluate technologies needed to realize them– allow a rough sketch

• Concepts follow function• Products follow concepts

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Functional Decomposition

• Technique used to define and refine product functions at all levels

• Function can be described in terms of– energy flow (mechanical, electrical, fluid,

thermal)– material flow (through-, diverging, converging)– information flow (mechanical & electrical

signals, software)

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Step 1: Find Overall Function

• Single, most important, statement of function based upon customer requirements

• Verb-noun-modifier form• Model using control volume approach

– system boundary– inflows, outflows– conservation of material, energy

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Step 2: Describe Subfunctions

• Decompose overall function using verb-noun-modifier description– Consider what, not how– List all alternative functions– Consider all operational sequences– Include all input and output energy, materials,

and information– “Post-it” note exercise

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Step 3: Order the Subfunctions

• Ordering may be chronological, spatial, disciplinary, or some other logic

• remove redundancy• finalize functional choices• eliminate functions not within system

boundary

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Step 4: Refine the Subfunctions

• Examine each subfunction to see if it can be further divided

• Decomposition ends when function becomes “atomic”, i.e., can be satisfied with an existing object or the invention of a new object

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Generating Concepts from Functions

• Recall: “concepts follow function”• Concepts can be represented by sketches,

block diagrams, verbal description, or models (paper, clay, etc.)

• Two-step process

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Step 1: Develop Concepts for Each Function

• Develop as many as possible• Should be able to generate at least three (3)

concepts for each refined function; if not– Re-examine function: “what” vs. “how”– Have ridiculous options been eliminated?– Is knowledge of function limited?

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Step 2: Combine Concepts

• Combine each possible concept from each function into “n” overall conceptual designs

• This generates (too) many possible designs• Some combinations will be mutually

incompatible, obviously inefficient, or ridiculous – eliminate these

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Sources for Concept Ideas

• Use existing information and designs!– Patents– Reference books– Trade journals– Research journals– Group brainstorming– Faculty, industry contacts

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Example: Tortilla Maker

• Primary Specifications:– Tortilla diameter: 101/2 (251.3 cm)– Tortilla thickness: 1/16 – 1/4 (1.6 – 6.4 mm)– Speed: 60 sec per tortilla (1/16)– Footprint size: 2 2 (60 cm 60 cm)– Weight: 10 lbs. (4.5 kg)

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Example: Tortilla Maker

• Features:– Auto start/stop with cancel function– Adjustable thickness– Adjustable cooking time– Easy cleaning: food handling parts removable

and dishwasher-safe

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Concept Evaluation (Ch. 8)

• Choose best concepts for development into a product (with limited information)

• Evaluation consists of comparison, followed by decision making

• Comparison can be absolute or relative• Two or more concepts may be developed in

parallel until relative merits become clear

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Evaluation Techniques

• Text suggests a sequence of steps for evaluating concepts and two different decision-making paths (Figure 8.1)

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Feasibility Judgment

• Gross judgement based upon intuition or “gut feel”

• Do not eliminate concepts for reasons such as “it’s too different” or “it’s already been done”

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Go - No Go Screening

• Customer requirements/engineering specifications – can they be satisfied with a given concept?

• Readiness of technology – is the technology (engineering & manufacturing) mature?

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Decision Matrix Method

• Semi-quantitative method for evaluating concepts (Tables 8.2, 8.3)

• Most effective when done by each team member

• Often requires iteration (repetition) as more is learned about the problem and concepts

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Robust Decision Making

• Robust – insensitive to uncertainty, incompleteness, and evolution of design

• Decisions based upon:– Satisfaction = belief that a concept meets the

criteria– Belief = knowledge + confidence– Figures 8.4-8.9, Tables 8.4, 8.5